Nucleotide sequence of a Populus tremuloides gene encoding bispecific caffeic acid/5-hydroxyferulic acid O-methyltransferase.

Bi-specific OMT (EC 2.1.1.68) catalyzes the meta-specific methylation of caffeic acid and 5-hydroxyferulic acid to ferulic acid and sinapic acid, respectively (Higuchi, 1990). It is one of the key enzymes in angiosperm dicots mediating the formation of unique precursors for syringyl lignin, which is generally absent in gymnosperms (Higuchi, 1990). OMT has been purified and its cDNA clones isolated from Populus tremuloides (Bugos et al., 1991, 19921, Populus deltoides X Populus trichocarpa (Dumas et al., 1992), and severa1 other plants (Gowri et al., 1991; Callazo et al., 1992; Jaeck et al., 1992; Pellegrini et al., 1993). In this paper we report the nucleotide sequence encoding an OMT genomic clone, designated PTOMT, obtained from a n angiosperm tree species. Two oligonucleotide primers corresponding to nucleotide positions 65 to 82 and to positions 1370 to 1388 of a full-length OMT cDNA (Ptomtl) from secondary developing xylem tissue of P. tremuloides (Bugos et al., 1991) were used for PCR using P. tremuloides total cellular DNA as a template. A 2.7-kb DNA fragment was amplified, subcloned, and sequenced in its entirety in both directions. The P. tremuloides POMT gene contains four exons and three introns (Table I). downstream from the translation start codon. The amino acid sequence derived from this P. tremuloides genomic DNA is 99.7% homologous with that from Ptomtl (Bugos et al., 1991).